Photosensitive resin plates for the manufacture of relief printing plates are preferably developable with water rather than organic solvent for various reasons such as ease of handling, health of workers who are in contact therewith, safety, and avoidance of environmental pollution. It is also very desirable to be able to use water based inks for printing with relief printing plates prepared from photosensitive resins, because oil based inks tend to mist and hence to cause health problems. In addition, the use of water based inks is favored in that the resulting print will not show through the printed paper from one side to the other and does not tend to rub off on the fingers.
There are various known photosensitive resin plates. The photosensitive resin compositions employed for conventional photosensitive resin plates are based on liquid unsaturated polyesters, polyvinyl alcohols, water soluble polyamides, cellulose acetate succinates, alcohol soluble polyamides, etc. All these materials, however, suffer from significant disadvantages. For instance, liquid unsaturated polyesters are inconvenient to handle and necessitate the use of an alkaline solution or a special air knife for developing. Polyvinyl alcohols and water soluble polyamides have extremely low resistance to water, and consequently water based inks are not usable with such resins. Cellulose acetate succinates require the use of an alkaline solution for development, and alcohol soluble polyamides require the use of an inflammable alcohol.
U.S. Pat. No. 3,801,328 (issued Apr. 2, 1974) discloses a water developable, photopolymerizable composition for preparation of a photosensitive resin plate. The disclosed composition comprises unsaturated ethylenic monomers, a photopolymerization initiator and a partially saponified polyvinyl acetate. This composition has been found to be developed very satisfactorily with water to give a relief printing plate. However, the water resistance of this relief printing plate at the surface is low, which in turn precludes its use with a water based ink.
Numerous other water developable, photopolymerizable compositions have been developed for the preparation of photosensitive resin plates. Each suffers from certain drawbacks, e.g., lack of sufficient water resistance to be useful with water based inks, lack of sufficient structural integrity to withstand the physical rigors of commercial printing operations, etc. Accordingly, what is still needed in the art are resins having improved chemical and physical properties.